Petroleum

Petroleum is a naturally occurring, yellow-to-black liquid found in geological formations beneath the Earth's surface. It is a fossil fuel, and is composed of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds. Petroleum is an important energy source because of its high energy density, and has long been used as a fuel in industry and transportation. It can be converted to other energy sources, such as kerosene, diesel, and gasoline, and it is also used as a feedstock in the production of plastics, asphalt, and other petroleum-derived products. Petroleum is also a major source of environmental pollution.